VA984Runner
Junior Member
I have a 1998 rear wheel drive 4Runner with the 3.4L engine. Mileage now is about 225,000. It started to stall this spring, which it has done before. I cleaned the Mass Air Flow Sensor, the throttle body, and the Idle Air Control Valve (IACV). After putting it back together it ran great except that I got a check engine light while idling at a stop light. The code was P0171 System Too Lean (Bank 1). I cleared the code and tested it again. It threw the same code again at idle. I then cleared the code and immediately went for a test on the highway. After thirty minutes, it ran great and there was no code. As soon as I got off the highway, although there was no stalling and no rough idle, it threw the same code the moment I was at a stop light.
I used throttle body cleaner with the extension tube on it to look for a vacuum leak with the engine running. The spray produced no change in idle until I sprayed it directly onto the joint between the throttle body and the upper intake manifold plenum. The engine stalled when I maintained a spray at this connection. Sorry, couldn't get the photo to upload.
I removed the throttle body, installed a new throttle body gasket, torqued the throttle body to spec, and reinstalled everything else. While I had everything out, I installed a new set of plugs. I test drove the 4Runner around town with the headlights and A/C on to load the engine as much as possible. The idle was very smooth and there was no stalling and no code. I'd recommend that if anyone is performing a service which requires the removal of the throttle body replace the metal throttle body gasket at the same time.
Here are the idle speeds based on the tachometer in the vehicle at full operating temperature:
In drive with the A/C on at a full stop with headlights on: 650 rpm
In drive with the A/C off at a full stop with headlights on: 700 rpm
In park with the A/C and headlights on: 700 rpm
I used throttle body cleaner with the extension tube on it to look for a vacuum leak with the engine running. The spray produced no change in idle until I sprayed it directly onto the joint between the throttle body and the upper intake manifold plenum. The engine stalled when I maintained a spray at this connection. Sorry, couldn't get the photo to upload.
I removed the throttle body, installed a new throttle body gasket, torqued the throttle body to spec, and reinstalled everything else. While I had everything out, I installed a new set of plugs. I test drove the 4Runner around town with the headlights and A/C on to load the engine as much as possible. The idle was very smooth and there was no stalling and no code. I'd recommend that if anyone is performing a service which requires the removal of the throttle body replace the metal throttle body gasket at the same time.
Here are the idle speeds based on the tachometer in the vehicle at full operating temperature:
In drive with the A/C on at a full stop with headlights on: 650 rpm
In drive with the A/C off at a full stop with headlights on: 700 rpm
In park with the A/C and headlights on: 700 rpm
